Appliance for measuring distances.



PATBNTED AUG. 25, 1908.

R. STRAUBEL.

APPLIANCE FOR MEASURING DISTANCES.

APPLICATION FILED MAR. 13, 1906.

RUDOLF STRAUBEL, OF JENA, GERMANY, ASSIGNCR TO TH E FIRM OF CARL ZEISS, OF JENA, GERMANY.

- APPLIANCE FOR MEASURINGDIS'TANCES.

Specification of Letters Patent.

Patented Aug. 25, 1908.

Application filed me. 13, 1906. Serial No. 305,875.

T 0 all whom it may concern:

Be it known that I, RUnoLF STRAUBEL, doctor of philosophy, a citizen of the German Empire, and residing at Carl-Zeiss strasse, Jena, in the Grand Duchy of Saxe-Weimar, Germany, have invented a new and useful ppliance for Measuring Distances, of which the following is a specification.

In the appliance for measuringdistances, which forms the subject matter of the present invention, a triple-reflector is made use of as object. The triplereflector (tripelspiegel) has been described by A. Beck in 1887 in the Z e-itschft far Instrumentenku'nde; It is a system 0 three plane mirrors upon which light impinges successively. A special form is the central-reflector tinguished by the three angles to each other. The central-reflector has the property of reflecting light along the same path that it entered the reflector. It will be seen that because of this property the central-reflector is inappropriate to the object of the present'invention In the British specification No. 21856 of 1903 H. Grubb treats of the applications of this centralreflector. He describes inter a-Zia its use for the measurement of distances by night, and in the following words: For obtaining ranges at night, the reflecting device is carried by a person at the place the range of which is required and is so held as to receive the luminous rays from a source of light exposed at the place where the range finder is located.

In contradistinction to Grubbs idea, the appliance for measuring distances according to the present invention is more simple, as it comprises only two essential components, the source of light at the place of observation and the triple-reflector at the target; the range finder being dispensed with. Moreover the triple-reflector is no central-reflector and is not only made use of as radiating object, but itself carries one of the terms, which serve to measure the distance, the angles between an incident pencil of light and its partial pencils reflected back again, or between these latter, acting in the capacity of angles of convergence. If these angles be known, it is only necessary at the place of observation to determine the linear distance between one partial pencil and another partial pencil (hereinafter designated pencil-distance) and the (zentralspiegel), displanes lying at right.

inclination of this line to one of the pencils in order to obtain by a well-known calculation the distance of the triple-reflector from the place of observation.

If the base line, that is, the line joining the two pencils, be made equally inclined to the two pencilsalmost at right angles, on account of the smallness of the angle of convergence-there results the distance required between triple-reflector and base line as the quotient derived from the encil-distance (more exactly, the pencil-distance at the place of observation, plus or minus the pencildistance at the reflector) and the angle of convergence between the pencils.

As already laid down' by A. Beck, out of one ray, which is incident upon the intersecting point of the three mirror surfaces the center of the triple-reflectorthere arise six partial rays for the location of which the following applies. If the incident ray be rotated in either sense about each of three axes of rotation, which passing through the center of the reflector have a variable position according to the angles formed by the three mirrors of the triple-reflector, and

-each time through an angle, which likewise depends upon the mirror angles and may be called magnitude of rotation, the said incident ray takes up the places of the six reflected partial rays one after the other. To each axis of rotation consequently correspond two rays, which lie symmetrical to the lane passing through the incident ray an the axis of rotation. If the magnitude of rotation be small, the two rays appertaining to the axis of rotation lie almost in one plane, and the incident'ray halves the angle between the two partial rays. partial rays lie approximately in pairs in three planes, which intersect each other along the incident ray. As at the same time the six rays lie in pairs symmetrically to the incident ray, instead of measuring the distance between two sufiices to measure the distance, half so great, of one or other of the partial rays from the incident ray.

For anygincident ray whatever, which does not pass through the center of the triplereflector, the places'of the six partial rays are deduced from the consideration, that to one incident pencil of parallel rays there paired partial rays, it

Then the six must be six emerging pencils of parallel rays to correspond. he directions of the partial rays, for any incident ray not passing through the center of the reflector, are therefore the same as for the ray passing through the center. of the places of the six partial rays, it is consequently only necessary to determine one point for each partial ray, through which the ray must pass. As such six points the image points, which would be produced by the triple-reflector from any point of the incident ray may be used; They can be found in the simplest way, if a straight line be drawn through the obj ectpoint in the in- I cident'ray and the center of the reflector and to this line as to an auxiliaryincident ray the six partial rays be constructed. The required image points he in these auxiliary partial rays at the same distance from the center of the reflector as the object point.

Knowing a single constant oft e triplerefiector, for example, a single angle of the reflector, is sufiicient to determine its other constants and its distance from the place of observation, provided that the encil-distance at the place of observation 18 large as compared with the pencil-distance at the reflector. Under the term constants of the triple-reflector is to be understood,-firstly, the constants of construction, namely, the three angles of the reflector, and secondly, three-constants of orientation independent one of another, for example, two independent angles necessary for the determination of the direction of one edge of the reflector and one of the angles of another'edge. In

, addition to one such constant of the reflector,

it must be known to which axis of rotation the pencils made use, of. are coordinated. The coordination of the pencils to the axes of rotation becomes apparent through each measurement, which exceeds the number of measurements necessary in case that coordination is otherwise known. I

7 One constant of the triple-reflector must necessarily be known to measure the distance, even ifall six pencils be measurable. In most cases all the constants of construction can be taken as known. On the other hand, it may be of interest to determine the distance with only one known constant of the reflector, that is, when this constant relates to the orientation of the reflector, for 'example, to the inclination of one of its axes of rotation to the incident pencil.

For the case first mentionedthat all the constants of construction of the triple-reflector are known-there may be specified how many and what measurements are to be undertaken with the-pencils for the determination of distance, since this case is relatively simple and at the same time practically important. 'It is ofcourse to be understood that at least one pencildistance must be For the complete determinationv base line. Since the angles of convergence of the pencils are dependent upon the position of the incident pencil to the axes of rotation and this position necessitates at least two data for its determination, there are besides the pencil-distance at least two angles still to be measured. These two angles must be only such as refer to the places of the pencils relativelyfto each other, where each angle can be substituted by a proportion of pencil-distances. The minimum of three measurements can then be performed in three different ways: There can be measured: (a) three encil dis-' tances, for example, those of al the three pairs of pencils, (b) one pencildistance and any two angles, for example, the pencildistance of a lpair and two angles between the planes of t e three pairs of. encils, (0) two pencil-distances and any ang e, for example, the pencil-distances of two angle between the planes of t ese two pairs of encils.

ince not all the data, which determine the places of the pencils relatively to each other, but only three of them independent one of another, are to be measured, only three pencils need to be accessible for measurement. Further, according to what has 0 been saidabove, since the incident pencil lies midway between the two pencils of a encil-pair, one partial pencil can at once be substituted by the incident pencil, and the distance determined with only two pencils accessible for measurement, but-not appertaining to .one and the same air.

It is of value that only t ee pencils are needed, knowing the coordination of the axes of rotation to the pencil pairs'by having recourse to the incident pencil or the locus of'the source of light .even only ,two not appertaining to one and the same pair airs and the when the 'place of observation is limited as to space, and further, when in consequence of coalescence not all the pencils appear separated. If there exist only four pencils, it is no longer uncertain which two axes of rotation come into consideration, for in this case there are only two axes of rotation at all.

If the tri le-reflector be filled up with a medium, w 'ch is more highly refractive than air and limited, moreover, by a plane GIItI'QLIICkk-filld exit surface (hereinafter designated entrance surface) as for instance, with a tetrahedron of glasswhich can, however, also completely take the place of the triple-reflectorthe conditions as regards the measurement of distance do not quite remain the same as before. However, knowing the construction of the tetrahedron, the places of the emerging pencils present suflicient data for determining its orientation with regard to the observer. Very simple and similar as in the case of the tripleobservation; its projection to the horizon will, however, be independent of the azi reflector proper, are the determinations, if

the entrance surface of the tetrahedron. The angles of convergence difler in this case from those, which would'correspond' to the triple reflector, only in index of refraction of the tetrahedron.

The orientation of the triple-reflector relatively to the observer is, deviating from the former supposition, in most cases wholly or in part known to the observer or can be even arbitrarily chosen by him. In all such,

cases it will be possible to determine the distance in a simpler 'manner. If the observer or the triple-reflector can move onlyin the plane,,in which the triple-reflector or the observer is likewise situated, the angle of convergenoe ofa pair of pencils can be made completely independent of the position of the incident pencil relatively to the triplereflector, so that the distance is found forthwith from the pencil-distance of this air. This is then exactly attained, if one 0t the axes, of rotation lie at right angles to the above plane. If in this case the reflector and the observer be not both in the plane of movement, but the incident pencil deviate 8 or less towards one side or the other of this plane, that is, within a region of 16,there would result an error of 0.5 per cent. in' the distance at most. Incidentally it may be said that in the triple-reflector one axis of rotation need .not absolutely lie perpendicular to the plane otmovement, in order to simply find the distance. For, if it lie, for instance, inclined to-the horizon,'which may be the plane of movement, the angle of convergence of the pencil-pair will then be dependent upon the azimuth of the place of muth and only dependent upon the inclination of the axis of rotation to the horizon.

In the tetrahedron the entrance-surface would be placed most suitably perpendicular to the plane of movement. There are two limiting cases to be taken intoconsiderati'on for the position of the axes of rotation in the tetrahedron, viz., one case in which one axis of rotation lies perpendicularto the plane of movement and the other in which one axis lies in this plane. If one axis of rotation lie perpendicular to the plane of movement and the distance.

for an index of refraction of 1.5 within a re.

parallel to the entrance-surface, then upon emergence of the pencil-pair belonging to this axis into'air there occurs an increase of divergencedependent upon the angle of incidence, and therefore the-inclination of theincident pencil with regard to the entrancesurface is needed to be known to determine It is easily found however, that gion of 40 about perpendicular incidence,'the maximum error does not exceed 2 per cent.,

proportion to the and within a region of 50 3 per cent. If the angle between the entrance-surface andthe incident pencil be determined approximately by the aid of a further measurement, then these two amounts can be sdmewhat reduced.

- If on the other hand one axis of rotation lie in the plane of movement, to which the entrance-surface is at rightangl'es, there occurs upon emergence into air one constant increase in the divergence of the pencil-pair,

dependent only upon the index of refraction. It is-necessary, however, in order to determine the distance, that the angle between-the incident pencil and the said axis of rotation is known, since the angle of convergence of thepencil-pair (in small magnitude of rotation) is proportional to the sine of this angle. If yet a second axis of rotation be laid exactly or approximately in the plane of movement, and if the angle between the two axes of rota: tion be known, then from the three data, the angle, the magnitude of rotation and the index of refraction, the distance andthe azimuth could be found. It is better, however, to have one-axis of rotation lying perpendicular to the plane of movement and one lyingin it-more especially on account of the intensity of light. If the index of refraction and the inclination of the entrance-surface to the axis of rotation lying in the plane of movement be ,known,-the relation between the pencil-distances supplies the angle of incidence in a very simple manner. For the determination of the direction, the magnitude of rotation, difficult of measurement in consequence of its diminutive size, need not be known. If such cases be dealt with, in which the tetrahedron can be always arbi trarilyorientated to the observer, in that, for example, it is being carried by another person, the simplest position may be given to the entrance-surface, namely, that perpendicular to the incident pencil, by means of a sighting device. slight rotation of the reflector, only. an in-i crease in divergence proportional to the index of refraction of the tetrahedron.

Since through the sub-division of the incident pencil into six emerging pencils, the energy of light is likewise divided, it is desirableto combine some of. the pencils and thereby increase theirintensity. If one axis of rotation of the triple-reflector coincide with another, then two pencil-pairs coalesceto form one pair, and four pencils onTy remain. If the third axis of rotation coincide with the double axis formed as above from the first and second, making a threefold axis, then There results then, in.

but two pencils remain, of' which each is,

originated through coalescence of three encils. Exact coalescence of all six pencils llltO one orresponds to the transformation of the triple-reflector into a central-reflector, which is inapplicable for the present method of measurement. The method is, however,

still practicable, when the coalescence is not quite complete, that is, overlapping of the cross sections of the pencils occurs at the place of observation. The three usable 5 cases, that 6, 4, 2 pencils (3, 2, 1 axes of rotation) exist, are realized by the construction of the triple-reflector with O, 1, 2 right angles resfectively.

f only one angle be a right angle, that is, there be only two axes of rotation, one simple and one double axis, then it depends upon the two other angles, how these axes of rotation lie to one another. Since the magnitude of rotation is of the same order as the excess of the largest angle over 90, and since at most a slight amount of the magnitude of rotation is desirable, the two angles hereafter shall be supposed to differ but a little from 90. The two axes in this case he approximately in the reflecting plane opposite the ri ht angle. The two limiting cases consist in, rstly that the two axes of rotation coincide .with one edge of the reflector, that is, a threefold axis occurs, and secondly, that the two axes of ro tation form a right angle one with the other, and in addition thereto have equal but opposite inclination with respect to the edge of the reflector. If the angles be'both-greater or both smaller than 90, then the double axis lies outside the reflector. If one be greater and the other smaller than 90, the double axis lies within.

In rectangular position of the two axes of rotation to one another, determination of distance becomes exceedingly simple. If that axis of rotation (simple or double) which lies outside the reflector, be placed at right angles to the plane of movement, then the other lies in the latter; the pencils corresponding to the first give, with the triple reflector, the distance immediately, in the case of the tetrahedron, as above mentioned, only in simple combination with the pencils of the other axis of rotation.

If the reflector system have a threefold axis and'correspondingly supply only two encils, then the edge of the reflector, which orms the axis of rotation, will be placed, so that the diagonal of the cube 'assing through the center of the reflector fa1l in the 'lane of movement, in order to intensify the i1 umination. If there be a tetrahedron having a threefold axis of rotation, the simplest way is to 55 lay the entrance-surface at right angles to the plane of movement and also at right angles to the projection of the edge, forming the axis of rotation, on this plane. In this arrangement are the distance of the tetrahedron and he angle, which the incident pencil forms with the entrance-surface, easily to be determined from two measured data, namely, the pencil-distance and the inclination be-' tween the plane of the pencils and the plane 65 of movement. '80 long as the incident penthe angle between the faces 906, which cil impinges approximately at right angles on the entrance-surface, one of the measurements, namely, the pencil-distance or its projection on the plane of movement, suflices.

In the annexed drawing: Figure 1 is an elevation ofa reflector forming part of an appliance according to the invention. Fig. 2 is a plan view of the said a pliance. Fig. 3 is a cross-section through t e total pencil entering the reflector. Fig. 4 is a cross-'section through the partial pencils emerging from the reflector. Fig. 5 is an elevation of the ap liance with cross-sections through the artiaFpencils at the place of observation.

ig. 6 is another lan view of the appliance, on a reduced sca e, showing the crossing of the partial pencils emerging irom the re-' flector The object at the distance to be measured is a glass tetrahedron A, Figs. 1 and 2, presenting a solid angle, approximately that of a cube, the three faces of which .meeting in the edges I, II'and III are the reflecting surfaces. The entrance surface a b c d e f stands at right angles to the diagonal of the cube. Of the three angles contained by the reflecting surfaces,-those two at the edges II and III are right angles, so that there ex- 1 ists only one single (threefold) axis of rotation lying in that edge the angle at which is not a right angle, '11. e., in the edge I. This angle at-I is smaller than but only by a very small amount'd, Fig. 1, If this amount and the index of refraction be known, all constants of construction of the tetrahedron are known. In Fig. 1 instead of the angles between the faces (at the edges I, II and III) the op osite angles between the edges are referred to, which in the present case are equal to them. The three corners of the tetrahedron at the entrance surface are truncated by plane sections, which lie perpendicular to this surface and give it the form of a hexagon a b. (:d of. r

Particulars regarding the position of the tetrahedron A to the horizon are afforded likewise by the Figs. 1 and 2, from which it will be seen that the entrance-surface a b c, d e f lies vertical, the diagonal of the cube horizontal. The edge I of the reflector with acts, as axis of rotation, lies above the diagonal of the cube in the same vertical plane. Further, if it begranted, that the source of light lie in the same straight line as the diagonal of-the cube, then the orientation of the tetrahedron with. respect to the source of light is also completely solved. In Fig. .2 the illuminating device is also represented,.which is a search light, 7.. a, a combination of a source of hght and an optical system, -which latter renders a portion of the raysemitted by .the source of hght parallel to one another and may be either a collective lens system or a concave mirror. 130

. cils are opposite to those of the This search light is in reality very far removed from the tetrahedron, even much farther off than would appear from Fig. 6. It is in this case supposed to consist of a parabolic mirror B with its axis in the same straight line as the diagonal of the cube, and of a point of light placed at the focus 9 of the mirror. The diameters of the tetrahedron A and of the reflector B are chosen, so that the pencil of rays parallel to the diagonal of the cube, which is produced by the illuminating device, on entering the tetrahedron completely fills the hexagonal aperture of the latter. In Figs. 2 and 6 the left and right halves of this pencil are distinguished by differently dotted rays, while the plane rimary pencil emitted in the vertical pane of the axis is characterized by a. full drawn rav.

The hexagonal pencil, which enters the tetrahedron, can be thought to be composed of six diflerent partial pencils, each of which meets the three reflectin surfaces in different order of sequence; Ihe total pencil is resolved into these six partial pencils by three planes of separation,- which intersect each other in the diagonal of the cube. Their three traces on the entrance-surface of the tetrahedron would coincide in 'the elevation Fig. 1 with the six interrupted lines drawn in the tetrahedron, of which lines the dashes' show the reflector edges I, 'II and III and those dotted the images of the former. Accordingly the cross section of the total entering pencil may be supposed to consist, as represented in Fig. 3, of=six quadrilateral partial sections a. 5 0 (1 e f. Upon their exit again out of the tetrahedron the partial pencils have attained the places as represented in cross section in Fig. 4. It is apparent that the places of the emerging partial penentering ones and that therefore the partial pencils 6 0 (1 admitted through the right half of the aperture of the tetrahedron emerge again through the left half and inversely, as indicated also in Figs. 2 and 6.

To the threefold axis of rotation of the tetrahedron corresponds a grouping of the six emerging partial pencils-into two triple partial pencils 6 0 (1 and e f a, which lie symmetrical to the axis of the entering total pencil. Of the above three planes of separation the vertical one decides the grouping, because it contains the axis of rotation I. The three partial pencils 6 0 d entering on the right hand of this plane and the otherthree e f a, entering on the left hand of it emerge left and ii ht respectively, again Te partial pencil. Since combined into atrip the angle at the edge I is less than aright angle, the two emerging tri le partial encils 6 0 (1 and e f a cross eac other. supposedin Figs. 2, 5 and 6 this has already taken place, long before the pencils arrive at the place of the illuminating device B, so that they pass by on either side of it. On account of the great inclination of the axis of rotation I with respect to the horizon and on account tion of the tetrahedron to the source of light and its constants of construction be known to the measurer, by which means then also the angle of convergence between the pencils is indirectly given. As mentioned in the commencement, the distance'is the quotient obtained from the pencil distance and the angle of convergence between the pencils. The distance between the pencils is accessible to direct measurement by fixing the places of' the margins of the pencils. The margin of a pencil is easily found by moving the head to and fro in the plane of the pencils transverselyto them, and in so doing observing with one eye in which position ofthe head occurs the appearance and extinction of the flash. In the present case, where the two triple partial pencils cross each other, the two outer margins of the cross sections of the pencils constitute, as indicated in Figs. 2 and 5, the pencil-distance h.

The outer margins are formed by the two plane primary pencils, which are originated from the plane primary pencil emitted from the illuminating mirror in the vertical plane of the axis, these three plane primary encils being represented in Figs. 2 and 6 full lines. The crossing line of the two emerging plane primary pencils passes through the center of the reflector, so that the pencil-distan ce at the reflector, which according to the rule given above shouldbe added to or subtracted from the pencil-distance at the place of observation, becomes zero. 1 1

'What I claim as my invention, and desire to secure by Letters Patent, is

1. The combination with a source of light .of a triple-reflector slightly deviating from a central-reflector in that the three reflecting surfaces include at least one angle which differs from 90.

2. The combination with a search light of aglass tetrahedron, three surfaces of which constitute nearly a central-reflector in that at least one of their three angles differs from 90 and the fourth surface of which forms equal angles with the three reflecting surfaces.

3. The combination with a source of light of a triple-reflector slightly deviating from a central-reflectorand so orientated to the horizon that an axis of rotation lies in a vertical plane. r

4. I The combination with a source of light name to this specification in the presence of of a triple-reflector, of the three angles of two subscribing witnesses.

which two areright angles and the third only RUDOLF STRAUBEL slightly deviates from a right angle, thisre- 5 flector being so orientated to the horizon that Witnesses:

the axis of rotation lies in a. vertical plane. PAUL KRi'IGER,

In testimony whereof I have'signed my FRITZ SANDER. 

